


Epoximise

by sapphire_eyes27



Category: Haikyuu!!
Genre: Alternate Universe - Harry Potter Setting, Alternate Universe - Hogwarts, Gen, Magic, Osamu's pov, Quidditch, Sibling Banter, Sibling Bonding, Sibling Love, and in sytherin, they're muggle-born
Language: English
Status: Completed
Published: 2018-01-22
Updated: 2018-01-22
Packaged: 2019-03-08 00:51:12
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,185
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13447011
Author URL: https://archiveofourown.org/users/sapphire_eyes27/pseuds/sapphire_eyes27
Summary: Epoximise- a Transfiguration spell that bonds two objects together;The first thing Osamu asks when Professor Tarou Oomi presents him with his acceptance letter to Hogwarts is, “Where’s ‘Tsumu’s?” because they’ve always been inseparable. There’s no Atsumu without Osamu; no Osamu without Atsumu. And it’s not about to change now.





	Epoximise

**Author's Note:**

> This is an expanded version of the fic I wrote for the Haikyuu!! Sibling Zine (it's free so please check it out [here](https://drive.google.com/file/d/1ToI4Jp2dtSNyw3nm41J_0VzUL4CdBgAY/view)!) I wanted to include more scenes which I couldn't in the zine version because of the word limit. I hope you all enjoy it!

Osamu is spiking his brother’s tosses in the backyard one cloudy afternoon when their mother calls them. He stares at her curiously because for the first time, the calm air around her is feigned. Her smile is tight, and the lines framing her eyes are tighter still.

“There’s someone here to see you, Osamu.” She offers nothing else, and all Osamu can do is follow her inside.

Atsumu doesn’t say anything but stays close to Osamu as they enter the living room. Before them sits a man they’ve never met before in a tailored pinstriped suit and glasses, sipping tea.

He eyes Osamu and Atsumu in surprise, probably not expecting to meet identical twins. He stands up with a smile and shakes both their hands nonetheless.

“This is Osamu,” Osamu’s father says, placing a hand behind the younger twin’s back.  

“Hello, Osamu,” the man greets. “My name is Tarou Oomi, and I am a professor at the Hogwarts School of Witchcraft and Wizardry.”

_Witchcraft and Wizardry?_ Osamu thinks. _Is this guy insane?_ His mother and father are both silent as the man speaks. _Do they actually believe this loon?_ He glances at Atsumu and can tell from the identical pale gold eyes staring back at him that they’re on the same page.

“I’ve never heard of that school probably because it doesn’t exist,” Osamu replies without the thought of any repercussions. “There’s no such thing as witchcraft and wizardry.”

“Osamu!” his mother hisses at his ill-manners.

The man seems unperturbed as he leans back against the sofa. “So, you’re telling me for these past couple of months there’s nothing odd going on with you?”

Osamu falters. Memories of floating leaves, fiery twigs and exploding rocks assault his mind. He’s never told anyone, not even Atsumu, the one closest to him, for fear of being ridiculed. Osamu always thought it was his mind playing tricks on him and kept the incidents a secret.

Tarou smirks at Osamu’s hesitation. “You’re a wizard, Osamu.” He pulls out a stick of the darkest wood Osamu has ever seen. “And so am I.”

Tarou touches the tip of his stick to the thick envelope resting on the coffee table. Osamu’s jaw drops when a second later the envelope opens itself up and the letter inside floats out before transforming itself into a paper airplane. It flies around their living room before landing on Osamu’s lap.

“Open it,” Tarou tells him, and Osamu does, noting how the paper remains creaseless.

Osamu feels Atsumu’s breath tickle the back of his neck as his brother too skims the contents of the letter over his shoulder.

It’s an acceptance letter to the school with his name clearly written at the top with the later portion highlighting the beginning of term and the supplies needed.

Osamu feels his heart hammer in his ribcage. Tarou is grinning now, and Osamu realizes why. In his moment of panic, the letter hovers above his palm, swaying with the gentle current in the room. His family stares at him in utter shock.

He sandwiches the paper between his hands and turns to Atsumu.

It’s like the floor has opened up beneath his feet, and he’s falling into an endless abyss.

Betrayal is carved onto every line of Atsumu’s face. His eyes are hard and cold, and Osamu feels tears burn the backs of his eyelids.

All Osamu can think about is his twin.

“What about ‘Tsumu?” Osamu asks Tarou, voice wavering slightly. “Where’s his letter?”

Tarou’s eyes widen as he struggles to find the right words. “Uh…your brother…doesn’t have one.”

_I’d be going without ‘Tsumu?_ Osamu thinks incredulously.

They’ve always been inseparable. There’s no Atsumu without Osamu; no Osamu without Atsumu. And it’s not about to change now.

He swallows the lump in his throat and straightens his back. Jabbing a thumb at his twin, he says, “If ‘Tsumu doesn’t go, I don’t go either!”

That is his ultimatum.

Osamu doesn’t listen to anything else Tarou might have to say because he’s already dragging his brother away to their room.

He has a lot of explaining to do. If only Atsumu would meet his eyes…

***

A week later, Atsumu receives his own acceptance letter to Hogwarts.

He finally looks at Osamu.

***

In the beginning of August, when the sunlight is already paling, Tarou takes the twins to Diagon Alley for their school supplies.

“Every young wizard needs a wand,” he explains to them, “So that is what we’re getting first.”

The inside of the wand shop looks a lot newer than the outside. The floors gleam in the bright candlelight and boxes line the entirety of the tall wall behind the counter. An old wandmaker with a wispy beard and his young assistant greet them.

The assistant measures Osamu’s dominant arm and relays the information to the wandmaker who then rifles through the hundreds of boxes for the right wand. He presents Osamu one with a curved base and a wood much too light for Osamu’s liking. He tries it nonetheless and ends up creating a vortex of parchment paper that sucks in everything in its path.

The wandmaker cleans the mess and quickly takes the wand back. “Maybe that is not the right one for you,” he says with an awkward chuckle and proceeds to show Osamu more wands.

After another fruitless attempt, Osamu finally finds one best suited for him. It’s twelve inches long with a phoenix feather core and made from hazel wood that’s almost as dark as Osamu’s hair. It’s sturdy and heavier than the ones he’d tried before, but the weight is reassuring as the wand sits like an extension of his arm.

Atsumu rocks on the balls of his feet the entire time, eagerly awaiting his turn. He doesn’t have to wait long before his arm, too, is being measured. When Atsumu tries the first wand, nothing happens. So, he tries another.

And another.

And _another_.

Osamu chews the inside of his cheek, a habit his mother has repeatedly scolded him for. Atsumu has been trying different wands for almost an hour, but the results are always the same. While Osamu can manipulate almost anything by merely pointing his wand, Atsumu can’t even move a hair.

“Maybe I’m too special for a wand,” Atsumu jokes, but Osamu can see the anxiety manifest in the tightness around his eyes.

“Don’t bet on it,” Osamu says, hoping to lighten the mood. “You haven’t even tried a tenth of the wands here.”

The words seem to do the trick as Atsumu’s eyes brighten with confidence, despite the pout on his lips.

Atsumu resumes his quest with renewed vigor. It takes the rejection of another half dozen wands before Atsumu points and asks about an old box in the corner. The young assistant pulls it out, careful to not disrupt the rotting edges, and hands it to the wandmaker.

Despite the deteriorating condition of the box, the wand inside is most definitely new. It’s made from a rich brown wood that turns auburn when it catches the light, and has a smooth handle unlike Osamu’s.

“I forgot we even had this,” the wandmaker confesses. “Looks like a twelve-inch redwood with a phoenix feather core.” The wand doesn’t budge when he tries to bend it. “Quite rigid, too.”

He hands it to Atsumu, whose mouth parts in joy as soon as his fingers wrap around the handle.

“This is it!” he exclaims. “This is my wand! I don’t know how to explain it, but it feels like—it feels like—”

“It feels like it’s a part of your hand,” Osamu finishes for him, and Atsumu grins.

“Yeah!”

“Told you you weren’t so special,” Osamu says as he fishes for the gold in his pocket.

“Shut up!”

Atsumu goes to poke his twin with his new wand, but Osamu is quick to use his own to deflect the blow.

When their wands touch, there’s a bright spark and a pop, like a crackle of electricity. For a second, Osamu thinks they’ve broken their wands and is about to pounce on Atsumu in anger before he sees golden tendrils of light erupt from the tips. The tendrils are as fine as spider’s silk and wrap around each other before weaving up their wandarms, seemingly binding them together.

Osamu feels not only one with his wand but also with something— _someone_ else. His wand and arm feel like they’re connected indefinitely to Atsumu’s. In fact, his whole _body_ feels like it’s connected to Atsumu’s. He doesn’t even know if they are still two separate people anymore. When he stares into his twin’s eyes, he isn’t sure if he’s looking at Atsumu or himself. It’s strange, this bond, but Osamu can feel the untapped, raw power within this connection like water ready to burst from behind a dam.

Within a few moments, the golden tendrils disappear, sinking into their skin, yet Osamu feels them mixing with his blood and thrumming in his veins. Atsumu is just as dumbfounded as to what is happening as Osamu is. They turn their equally astonished expressions to the wandmaker for an explanation.

“Merlin’s beard…” he whispers, mouth parted and sunken eyes gleaming. “Never in all my life…”

The wandmaker’s assistant is at a loss for words just as much as he is.

“Um, this isn’t normal, is it?” Atsumu asks.

“No,” the wandmaker says with glee. “No, it most certainly isn’t! It looks like the feathers in your wand cores come from the same phoenix. I did not think that was even possible!”

Osamu stares at his wand with a mixture of wonder and apprehension. “Is it still safe to use?”

The wandmaker laughs as if it’s the silliest thing he’s ever heard. “Of course, it is, my boy!” He extends his hand, asking for both Osamu and Atsumu’s wands. “I’ll have these packed for you right away.”

The twins hand them to him, and Atsumu whispers to Osamu, “Why is he so surprised? He’s the wandmaker, isn’t he? Shouldn’t he already know where each of the parts come from?”

Osamu shrugs his shoulders, not equipped with an answer, and hands the gold to the assistant.

***

The months fly by faster than either of them care to admit, and soon they’re stepping off the boats with the rest of the first years, waiting for the front doors of the castle to open.

As soon as they enter, Osamu realizes why it’s called “The Great Hall”, because it really _is_ the greatest thing he’s ever seen.

Hundreds of candles float above the tables, and the ceiling is sprinkled with thousands of twinkling stars that look like they could fall onto his palm at any moment. Everything is so bright that Osamu fears he might go blind.

The new students stand in the center as the Headmaster begins with the opening remarks, and all too soon, the Sorting Hat is brought out. Osamu’s heart practically beats out of his chest at the sight of it. Atsumu had asked him on the train which house he’d want to be sorted into, but truly, Osamu had no clue. He did know one thing for sure though: he didn’t want to be separated from his twin.

Halfway through the sorting, Atsumu’s name is called. He walks to the stool, head held high and gait full of confidence. Osamu chews the inside of his cheek in anticipation, but he doesn’t have to wait long. The hat barely touches Atsumu’s head before it shouts, “Slytherin!”, clear and sharp throughout the hall. The table to Osamu’s left erupts into applause, and a grinning Atsumu takes a seat towards the front.

Osamu’s name is called next, and his brother gives him a thumbs up when he passes him. Up close, the hat looks much more worn and faded, as if left out in the sun for too long, and Osamu can make out what can only be described as furrowed eyebrows and a frown embedded within the creases.

He gingerly takes a seat, and the hat is placed on his head. He closes his eyes and waits for the verdict, but his thoughts are repeating only one word: _Slytherin, Slytherin, Slytherin!_

“Slytherin, huh?” a voice says in his ear, and Osamu nearly falls off the stool before he realizes it’s the hat speaking. “But you have the mind and temperament befitting a Ravenclaw. Are you sure you want to follow your twin?”

_I don’t want to leave him alone_ , Osamu thinks, but it doesn’t sound right, even to him.

“Do you think he cannot grow without you?” the hat asks, words underlined with interest.

The thought is fleeting, but Osamu knows the hat has picked up on it.

_Maybe I need him more than he needs me._

“Slytherin!”

The sound from the serpentine house is deafening, and he thinks Atsumu yells the loudest, sporting a beaming face that matches his own.

***

Osamu doesn’t know what causes him to wake up so late at night. Perhaps it’s the cold biting at his bare toes, or the feeling he’s forgotten to do something. He knows he should go back to sleep with class so early in the morning, but how can he when the bed next to his is empty? Atsumu is prone to sleep like the dead. Where could he possibly be at this hour?

Osamu dons his robe and slippers and makes his way down to the common room. It’s even colder out here with no fire heating the hearth. He shivers and almost misses the hunched figure sitting by the dying embers.

Atsumu’s wand is out and a feather lies on the floor beside him. His expression is pinched in frustration as he waves his wand and utters a spell. The feather remains motionless as if mocking him. He growls, beating the feather with his wand, before collapsing onto his back in defeat.

“Didn’t know you cared so much about Charms,” Osamu finally says, and almost laughs when Atsumu flinches from the sudden sound. His amusement is short-lived because Atsumu recovers instantly.   

“I don’t,” he quips. “But I hate it when my little brother is better at something than me.”

Osamu exaggerates the eye roll and plops down next to Atsumu. “You’re only two minutes and forty-eight seconds older than me. Stop acting like it’s a big deal.”

Atsumu scoffs. “Like you wouldn’t lord it over me if you were older.”

He’s right, of course, but like hell Osamu would admit it.

"Let me see how you're doing it," Osamu says because no matter how nonchalant Atsumu seems, Osamu knows it’s eating away at him. 

"It's ok, _little brother_ ," Atsumu pats Osamu's head condescendingly. Osamu swats his hand away as his brother laughs, standing. "That's enough practice for one night. I'm going to bed."

"Trust me, no amount of beauty sleep will help that face. Might as well show me," Osamu goads.

Atsumu glares at him. "We have the _same face_."

"I'm still the better-looking twin though," Osamu replies, quick as a whip.

A smile tugs at the corner of Atsumu’s lips as he sits back down. “Cheeky brat.”

“Thank you!~”

“It wasn’t a compliment! Now, shut up and tell me what I’m doing wrong!”

“It’s all in the wrist.”

Osamu demonstrates the correct movement with his wand, and Atsumu mimics it while uttering the spell. He feels a deep-rooted sense of accomplishment when Atsumu’s feather finally floats towards the ceiling.

***

Osamu is like a jack-of-all trades, master of none, when it comes to the Hogwarts subjects, unlike Atsumu.

From day one of Flying, Atsumu has excelled, like a bird taking to the skies after years of confinement. He’s a natural, flying as if he was born with a broom in his hand.

“You should try out for the Quidditch team,” Tarou tells an overjoyed Atsumu, who’s had a particularly successful and thrilling experience chasing after an enchanted pebble in front of their head of house. “Our team could use someone fast and agile like you.”

During their second year, he decides to, but on one condition.

“Try out with me,” Atsumu commands—always commands—Osamu.

Osamu doesn’t mind; he, too, likes Quidditch, and he missed playing a sport with his brother. But he’s had eyes for only one position ever since he saw his first match.

“Are you sure about that?” He smirks. “You’ll be up against me, after all.”

Atsumu’s grin is downright menacing. “That’s why victory’s gonna taste even sweeter when I crush my little brother into the dust.”

***

A week after the tryouts, the seventh year Slytherin Quidditch captain, Ishikawa Alex, asks Osamu to meet him on the pitch after his last class of the day.

The wind howls in Osamu’s ear and stabs at his face with what feels like hundreds of tiny needles as he trudges to his destination. Despite it still being September, the cold is unrelenting, and Osamu surmises winter will come early this year. He’s going to have to make sure Atsumu stays bundled up at all times because his twin has an annoying habit of never wearing warm clothes and then whining when he catches a cold.

He stuffs his hands deeper into his jacket pockets and continues walking, wondering why Alex wants to speak to him. He has an idea though. Osamu hopes he doesn’t look too crestfallen and embarrass himself in front of his upperclassman.

Alex is doing laps around the perimeter of the pitch, whizzing past imaginary opponents like lightning on his Dragonspeed X, a broom Osamu’s parents has promised to buy them both when they made the team.

When he sees Osamu, Alex descends from the sky and slaps Osamu good-naturedly on the shoulder. “Hey, you made it!”

“Of course,” Osamu says, refusing to rub his shoulder to ease the pain and appear weak. Alex is much bigger than he is and doesn’t realize that his usual roughhousing can be a bit too much. “What is it that you wanted to talk about?”

“Straight to the point I see.” Alex grins and shifts his broom to the other hand. “Don’t worry, it’s good news, so no need to look so constipated.” He chuckles at his own joke before continuing. “You made the team! I’ve decided that you’ll be our Seeker.”

“What?” Osamu asks, dumbfounded.

“You’re gonna be Syltherin’s Seeker,” Alex repeats.

“But I didn’t even catch the Snitch during the tryout match,” Osamu says. “It was Atsumu.”

“I know, but I just don’t see Atsumu mixing with the team,” Alex explains, dark eyes serious. “He’s too stubborn and hard to control. I can’t have him doing whatever he wants. I pride myself in figuring out people’s strengths and weaknesses in Quidditch, but I cannot see Atsumu working with us. His selfish nature far outweighs his strengths. There’s more to being a Quidditch player than just being a fast flyer.”

“You are completely overlooking his tenacity and passion for the sport,” Osamu retorts icily. No one insults his brother like that. Only Osamu has that right. “He may be selfish, but that’s only because he hates losing. If you’re looking to exert your control, I suggest you fill your team with puppets instead of people. I don’t want to be a part of this team if you’re the one leading us.”

“Wait!” Alex calls after him just as Osamu turns away. Osamu pauses but doesn’t regard him any further. “I really want us to win the Quidditch Cup this year, but I know I cannot do it alone. I—I’ll give Atsumu a chance, but I also want you on the team. I do think you’re an asset. You can have whichever position you want, so just—just think about it.”

Osamu walks off without saying anything.

***

A few days after the meeting on the pitch, Atsumu storms into their dormitory where Osamu is reading on his bed.

“I don’t need to be coddled, and I definitely don’t need your pity!” he seethes, eyes blazing with fury.

Osamu remains silent because he knows what Atsumu is talking about. He didn’t expect Alex to spill the secret to his twin, but the damage is done.

“Did you think I’d throw some kind of temper tantrum like a five-year-old because you got Seeker, and I didn’t?” Atsumu rages. “How dare you bow out to preserve _my_ feelings?”

Osamu lowers his book, knowing his calmness is pissing off Atsumu even more, but there’s already enough anger in the room.

“The captain was underestimating your skill,” Osamu says with a level gaze. “And that annoyed me. I just want him to eat his own words when you win us the Quidditch Cup.”

“And they say I’m the petty twin,” Atsumu huffs.

“Oh, you still are,” Osamu says, resuming his reading because he knows he’s made the right decision. Atsumu just needs time to realize it, too.  

***

It’s spring and the grass on the Quidditch pitch is crisp and fresh under Osamu’s feet.

After months of brutal training and many arduous matches, they’ve finally made it to the final against their fated rival, Gryffindor.

As soon as the whistle blows, the players whirl into motion, and Osamu is already chasing after the Quaffle. The exhilaration from flying takes over, pumping the adrenaline through his veins like the very first time he jetted off into the sky. The spectators melt away as Osamu dodges Bludgers and other players. From the corner of his eye, he can make out his fellow Chasers helping him.

Osamu may not be as fast a flyer as Atsumu, but he can still hold his own. In no time, he catches up to Gryffindor’s Chaser and steals the Quaffle from her grasp before dashing off in the opposite direction. He scores the first points of the game, and the Slytherin spectators cheer and chant his name.

They maintain the led for the better part of an hour before things start going downhill. Gryffindor’s Chasers are relentless and sneaky as they jump from one strategy to another which means Osamu can never guess what they’re going to do next. Soon, it’s Slytherin who’s trailing after Gryffindor.

Osamu grows increasingly frustrated. It’s not like they haven’t played against Gryffindor before, but today their rivals are playing even more unpredictably. Little by little, the Slytherin Chasers close the gap until Osamu’s Quaffle whizzes through the goalpost, and they’re only twenty points behind.

As he returns to defend, Osamu catches sight of Atsumu, who’s a blur of green as he flies after the Snitch. The opposing Seeker is right on his tail, but if Atsumu just extends his fingertips a millimeter more, they’ll win the Quidditch Cup after six years.

The crowd suddenly grows louder, egging Atsumu on, and Osamu feels a triumphant smirk overtake his face. They’ve got this in the bag.

He’s so distracted that he doesn’t notice the Bludger hurtling towards him until it’s too late. He freezes in terror, eyes going wide and zeroing in on the iron ball before the cheers fade with the wind and his mind goes blissfully blank.

***

Before he even opens his eyes, the first thing Osamu feels is the soreness in his jaw. He moves it, and groans when the pain worsens.

“‘Samu! You’re finally awake!” Atsumu’s relieved voice cuts through his suffering, and Osamu opens his eyes, squinting against the dying sunlight that’s leaking in through a gap in the curtains.

His brother is kneeling beside his bed in the infirmary, still clad in Quidditch robes with his hair in disarray and his eyes puffy. Osamu feels dizzy when he remembers the last moments of the match.

“Did—did we win?” Osamu croaks. It hurts to talk, but he has to know—he has to know if his injury was in vain.

Atsumu looks away guiltily, and Osamu’s stomach sinks.

“You were falling so fast,” Atsumu says, voice low enough that Osamu can barely hear him. “I had to save you! Otherwise, —”  

Osamu closes his eyes and sighs. “I can’t believe I had to be saved by my brother. How uncool.”

He can feel Atsumu’s glare burn into his face. “I should’ve let you fall, you ungrateful little cockroach! You honestly deserved it for spacing out _during a match_!”

Osamu decides to be kind for once by extending an olive branch.

“Thanks,” he says, giving Atsumu a genuine smile.

He expects his brother to milk this rare opportunity for all its worth, but he’s surprised.

Atsumu seems to grow smaller as his forehead touches the bedsheets. “I’m sorry I couldn’t win us the Quidditch Cup.” He sounds crushed, like when he first found out Osamu would be going to Hogwarts without him.

“Don’t be such a cry baby, _big brother_.” Osamu chides, rolling his eyes. He raises his fist against the protest of his shoulder. “There’s always next year.”

Atsumu’s head snaps back up as a wobbly grin replaces his frown. “And next time, you’d better pay more attention, idiot. I won’t catch you twice.”

He bumps Osamu’s fist with his own, like a promise, and Osamu knows he’ll have no trouble keeping it.  

**Author's Note:**

> This is my first fic of 2018 so do be kind and leave me kudos, comments, criticisms, etc!  
> Or come say hi on my [tumblr](http://www.rolling-blunder.tumblr.com)!


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